Can Someone Explain the Fruit Thing to Me?

The Roman emperor Constantius II, son of Constantine the Great, died of illness in October or November 361 AD.  After relating the circumstances of his death, in Book XXI of his great history of the later Roman empire the Roman historian Ammianus Marcellinus sums up Constantius' "good and bad qualities."

The description of the good qualities ends with the following (emphasis added):

In riding, in hurling the javelin, and especially in the skilful use of the bow, and in all the exercises of the foot-soldiers, he was an adept. That no one ever saw him wipe his mouth or nose in public, or spit, or turn his face in either direction, or that so long as he lived he never tasted fruit, I leave unmentioned, since it has often been related.

Equitandi et iaculandi, maximeque perite dirigendi sagittas, artiumque armaturae pedestris perquam scientissimus. Quod autem nec tersisse umquam nares in publico nec spuisse nec transtulisse in partem alterutram vultum aliquando est visus, nec pomorum quoad vixerat gustaverit, ut dicta saepius praetermitto.

OK, I get that it's admirable for an emperor not to wipe his nose in public or spit.  But what's with the fruit thing?

UPDATE.  It turns out that there's a learned academic article on this precise issue:  Why Didn't Constantius II Eat Fruit? Unfortunately, it's on JSTOR, so I can't read it!